Leisure-time physical activity and risk of incident cardiovascular disease in Chinese retired adults

The optimum amounts and types of leisure-time physical activity (LTPA) for cardiovascular disease (CVD) prevention among Chinese retired adults are unclear. The prospective study enrolled 26,584 participants (mean age [SD]: 63.3 [8.4]) without baseline disease from the Dongfeng-Tongji cohort in 2013. Cox-proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). During a mean 5.0 (1.5) years of follow-up, 5704 incident CVD cases were documented. Compared with less than 7.5 metabolic equivalent of task-hours per week (MET-hours/week) of LTPA, participating LTPA for 22.5–37.5 MET-hours/week, which was equivalent to 3 to 5 times the world health organization (WHO) recommended minimum, was associated with a 18% (95% CI 9 to 25%) lower CVD risk; however, no significant additional benefit was gained when exceeding 37.5 MET-hours/week. Each log10 increment of MET-hours/week in square dancing and cycling was associated with 11% (95% CI 2 to 20%) and 32% (95% CI 21 to 41%), respectively, lower risk of incident CVD. In Chinese retired adults, higher LTPA levels were associated with lower CVD risk, with a benefit threshold at 3 to 5 times the recommended physical activity minimum. Encouraging participation in square dancing and cycling might gain favourable cardiovascular benefits.

). For example, ball games were assigned 1/3 weights by calculating the mean MET intensity of the specific LTPA types (basketball, tennis, soccer). "missing data" for LTPA was defined as missing one of the follow questions: 1 Type of LTPA; 2 Frequency of LTPA; 3 Duration of LTPA.
Implausible information for LTPA was those participating LTPA for over 12 hours per day or reporting no LTPA, but values>0 in the frequency or duration variables of at least one type of LTPA.
For assessment of sedentary behaviour, each participant was asked to provide their daily average time spent sitting at home on screen activities, including watching TV, VCR, and computer. We also asked participants: "In the past year, how many times per week did you play Mahjong?" Participants who reported at least once per week were further asked: "On average, about how many hours each time did you play Mahjong?". The weekly average time spent on playing Mahjong was calculated by multiplying frequency and time spent on playing Mahjong.

Assessment of covariates
Weight-related indicators were measured in light clothing without shoes. Body mass index (BMI) was calculated as weight (kilogram) divided by height (meter) squared. Current smokers were defined as smoking at least one cigarette per day for more than half a year. Current drinkers were defined as drinking alcohol at least one time per week for more than half a year. Family history of CVD including CHD and stroke was limited to first-degree family members. Hypertension was defined as being on anti-hypertensive medication, a systolic blood pressure >= 140 mmHg, a diastolic blood pressure >= 90 mmHg or a self-reported physician diagnosis. Hyperlipidemia was defined as total cholesterol >= 6.22 mmol /L, triglycerides >= 2.26 mmol/L, High-density lipoprotein cholesterol (HDL-C) < 1.04 mmol/L, low-density lipoprotein cholesterol (LDL-C) >= 4.14 mmol/L, medication use or a previous physician diagnosis. Diabetes was defined by fasting glucose >= 7.0 mmol/L or haemoglobin A1c (HbA1c) >= 6.5% or self-reported use of anti-diabetic medications (oral hypoglycemic medication or insulin). An overnight fast blood sample was collected by Sinopharm Dongfeng hospital. All biochemical blood indicators were measured using ARCHITECT ci8200, Abbott, USA. Missing values were replaced by mean or median, furtherly adjusted for dichotomous variables.

Detailed statistical analysis
The present study excluded 10254 participants with CHD (n=6457), stroke (n=2406), and severely abnormal electrocardiogram (n=838; severe abnormal electrocardiogram including atrial fibrillation, atrial flutter, pre-excitation syndrome, pacemaker rhythm, frequent premature ventricular contractions) 3 (Table 1). Cox proportional hazards regression models were used to calculate HRs and 95% confidence intervals (CIs) for cardiovascular diseases associated with baseline LTPA (Table 2). Analyses were adjusted for age and sex (model 1) and additionally adjusted for education, BMI, smoking status, alcohol intake status, hypertension, hyperlipidemia, diabetes, diet frequency (meat, fruit, vegetables), MET-hours/week, total sedentary time and family history of CVD (model 2). The reference group came from those below the minimum WHO recommended physical activity level (7.5 MET-hours/week).
Stratification analyses for associations between LTPA and incident CVD according to several potential confounders were presented in the Supplementary Fig.   S1. In addition, the dose-response analyses of square dancing stratified by gender were presented in Supplementary Fig. S2.
We also explored the additive interaction of LTPA and sedentary behaviour (including screen activities and playing Mahjong), using those who were the most physically active (> 36 MET-hours/week of LTPA plus 0 hours/week for Mahjong or 0 hours/week for screen activities) as the reference group (Fig. 3). The risk of sedentary behaviour with CVD was presented in Supplementary Table S2 categorized by none and median of sedentary behaviour time.
Sensitivity analyses were conducted by extended adjustment for household activity; excluding participants reporting over 6 hours of LTPA per day (n=189); excluding CVD cases (n=665) occurred during the first year of follow-up; excluding participants retired 5 years before the mandatory age for retirement (n=5882; 55 years for male and 50 years for female; Supplementary Table S1).
All statistical analyses were performed using the SAS 9.4 software package (SAS Institute, Cary, North Carolina, USA). A two-sided test and P < 0.05 was considered statistically significant. Table S1. Adjusted hazard ratios for CVD associated with leisure-time physical activity after extended adjustments or further exclusions.

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